fix "tkill" check

fix "tkill" check

An earlier patch removed the check for "syscall" since the results
were not used in the C code.  However, the result was used, via the
cache variable, elsewhere in configure.

This patch fixes the problem by checking for "syscall" at the point at
which HAVE_TKILL_SYSCALL is defined.

2013-11-11  Tom Tromey  <tromey@redhat.com>

	* config.in, configure: Rebuild.
	* configure.ac (HAVE_TKILL_SYSCALL): Check for "syscall".